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Date: Sat, 17 Feb 2007 19:56:34 +0100
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: [Xenomai-core] Re: Magics of [CAN] message filtering
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To: Wolfgang Grandegger <wg@domain.hid>
Cc: socketcan-core@domain.hid, Oliver Hartkopp <socketcan@domain.hid>, xenomai-core <xenomai@xenomai.org>

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Wolfgang Grandegger wrote:
> Jan Kiszka wrote:
>> Oliver Hartkopp wrote:
>>> When you're touching anything inside your API, have you ever thought =
to add
>>>
>>> __attribute__ ((aligned(8)))
>>>
>>> to the data[8] element of the struct can_frame?
>>>
>>> This would enable you to make 64 bit compares directly in the data
>>> section of the can_frame ...
>>>
>>> typedef __u32 canid_t;
>>>
>>> struct can_frame {
>>>     canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
>>>     __u8    can_dlc; /* data length code: 0 .. 8 */
>>>     __u8    data[8] __attribute__ ((aligned(8)));
>>> };
>> [Swallowing down my well-known opinion on typeof(can_dlc) :)]
>>
>> Yes, this should be done, already for the more urging sake of
>> unambiguous layout of the structure across the kernel/user space borde=
r.
>=20
> Is this not already the case? At least the size of struct can_frame is =

> 16 bytes.

On all target archs? With all supported compilers? Better make it explici=
t.

Jan


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